The present invention relates to an improved electrical water heating device for use in a closed-circuit heating system such as, for example, a central heating system.
The expression "central heating system" as used hereinafter, includes all the systems in which a liquid, such as water, is circulated through a closed circuit as a heat transfer agent. Such systems generally comprise a heating device in which the liquid is heated, a plurality of radiators connected to the heating device and a pump for circulating the liquid from the heating device to the radiators and vice versa.
That kind of well known heating system presents several practical and economical drawbacks that are associated either to the high coefficient of expansion of the water or, in the particular case of the heating systems using an electrical element to heat the water, the difficulties encountered for obtaining a uniform heating of the liquid inside the device.
Up to now, the first drawback mentioned above has been overcome by using an expansion tank opened to the atmosphere and providing an additional water supply in the circuit to compensate the loss of water that may happen by evaporation. Such an improved system nevertheless involves a permanent control of the level of water in the expansion tank to avoid overheating of the circuit for lack of water. For this reason, it has also been proposed to use a liquid having a very low coefficient of expansion, such as a vegetable or mineral oil, in a conventional heating system to make the presence of an expansion tank unnecessary. The latter arrangement has unfortunately the drawback of being very expensive because of the cost of the oils that can be used.
In order to overcome the second drawback mentioned above, namely the difficulties encountered for obtaining a uniform heating of the liquid inside the device, several electrical devices have been proposed, all provided with baffles or nozzles to increase the period of time during which water is in contact with the electrical elements, or to ensure a better distribution of water at the vicinity of these elements. An example of such an improved electrical heating device is disclosed in the U.S. Pat. No. 3,868,494, issued on Feb. 25, 1975 in the name of A. Pepin.
Unfortunately, none of these known devices has proved to be fully satisfying.
In particular, none of the known devices which comprise a plurality of heating elements obtain uniform heating of water inside the heater if one of the elements fails or is voluntarily inactuated by the consumer when the same decides to lower the heating temperature such as, for example, in the springtime.
None of the known devices ensures perfect circulation of water inside the body of the heater. This results in the presence of cold or warm water zones, located in particular in the corner of the body, and of hot or boiling water zones, located in particular in the middle of the body. The coexistence of such zones of different temperatures leads to thermal shocks that damage the apparatus and may be responsible for the annoying noises that can be heard with almost every known electrical water heating device.